Currently compressor driven heat pumps are mainly used for heating of e.g. houses and hot tap water. The characterizing feature of such a heat pump is that a liquid boils in the evaporator, whereby heat is taken up at low temperature and low pressure. The compressor pumps the gas from the evaporator into the condenser. In the condenser the gas is condensed to liquid, whereby heat is released at high temperature and high pressure. The liquid is returned to the evaporator via a restriction device.
However, the efficiency of the compressor is strongly dependent on the pressure difference across it, in the sense that the efficiency decreases drastically with increased pressure difference over the compressor.
A heat factor, F, of a heat pump is defined as the ratio between the heat delivered by the heat pump and the operating energy supplied to the heat pump. A normal yearly average of this heat factor for one compression-evaporation cycle is 2-2.5.
One way of increasing the heat factor is to lower the pressure difference across the compressor. This can be achieved by using a two component refrigerant, where one component comprises a gas being absorbed by the other component, which comprises a liquid.
A process utilizing such a two component refrigerant is operated as follows.
In the desorbator gas is released from the liquid, whereby heat is taken up at a low temperature and at a pressure corresponding to the concentration in the desorbator. The gas is pumped off by the compressor into the absorbator, where it again is absorbed by the liquid. In this process heat is released at high temperature and a pressure corresponding to the temperature and the concentration in the absorbator.
The liquid in the absorbator must not to be saturated with gas, because it would increase the pressure excessively in the absorbator, which of course is undesirable. Also the liquid in the desorbator must not be depleted of gas, because this would decrease the pressure in the desorbator too much. These two effects would cause the pressure difference across the compressor to increase. In order to prevent this to happen, liquid is pumped off by a liquid pump from the desorbator to the absorbator via a countercurrent heat exchanger. To prevent all liquid from collecting in the absorbator, liquid is drawn off via the heat exchanger and a restriction means from the absorbator to the desorbator. This is an entirely closed circulation system.
The two component refrigerant that is used is ammonia-water.
In DE-530 406 there is disclosed a method of generating cold comprising a compression refrigerating machine, operating with the ammonia-water system, wherein the compressor has been placed in the absorption liquid, in order to reduce noise, and to obtain improved cooling. Furthermore, in the disclosed device the condenser is also located within he absorption liquid, which is said to improve performance.
In SU-548005 there is disclosed a two-stage absorption compression refrigeration unit, wherein the compressor is placed inside the generator for cooling purposes, thereby improving economy.
In DE-31 29 957 there is disclosed a refrigerating machine operating with e.g. ammonia-water, and wherein the compressor has been integrated in the absorber unit.
A problem with prior art devices as discussed above, and the commercial heat pumps of today is the economy. The Carnot-efficiency is far from the optimum, and even very small improvements in this efficiency, say by 1-3%, require that substantial investments in improvements would have to made, and the equipment would therefore be too expensive to be commercially viable.
Another technical problem with the refrigerant system ammonia-water is its corrosive nature. Electrical and mechanical equipment such as pumps, and compressors and associated motors, will be subjected to an aggressive environment, and their operative life may be unduly shortened.
A drawback with current heat pumps is the necessity to cool the compressors. This is normally achieved by flowing air, but it often happens that temperatures in the vicinity of 100.degree. C. and above are reached, which may lead to so called coking of the lubricant in the compressor.